Driving circuitry for a vcSEL unit

Abstract

Disclosed is a driving circuit system for a VCSEL unit. The driving circuit system for the VCSEL unit comprises a charging circuit module, a driving circuit module, and a field effect transistor electrically connected to the charging circuit module and the driving circuit module. The field effect transistor is configured to be switchably operated between a cutoff position and a conducting position. When the field effect transistor is in the conducting position, a power supply unit of the charging circuit module charges an energy storage inductor. When the field effect transistor is in the cutoff position, the charged energy storage inductor provides current to a filter capacitor and a parasitic inductor of the driving circuit module, respectively. The driving circuit system for the VCSEL unit uses the energy storage inductor to increase the voltage acting on the VCSEL, so that the working current flowing through the VCSEL reaches a predetermined value with a predetermined rising time.

Description

Technical Field

[0001] This application relates to the field of lidar, and more specifically, to a driving circuit system for VCSEL units. Background Technology

[0002] Laser radar (LiDAR) is a type of radar that uses laser light as its detection signal. It emits a laser beam into a target area and receives the reflected signal to detect the relative position and distance of objects (e.g., obstacles) within that area, thereby enabling the detection, tracking, and identification of these objects. In recent years, LiDAR has been widely used in intelligent transportation, environmental monitoring, and military security. For example, LiDAR is used in intelligent driving perception systems for vehicles to detect obstacles in the road.

[0003] Specifically, the working principle of lidar is as follows: a laser (e.g., a VCSEL laser) emits laser pulses towards the target area and receives laser pulses reflected from obstacles in the target area. Based on the time difference between the emitted and received laser pulses and the speed of light, the distance between the obstacle and the lidar is obtained. A VCSEL laser (Vertical-Cavity Surface-Emitting Laser) is a semiconductor laser. Compared to traditional edge-emitting semiconductor lasers, it features high fiber coupling efficiency, low power consumption, low temperature drift, small size, and ease of integration and packaging.

[0004] For lidar, the emission power of the laser determines the ranging range, while eye protection requirements limit the power of the lidar. To resolve this contradiction, it is necessary to have a large emission power in a very short pulse time, and at the same time, reduce the duty cycle of the pulse time, thereby reducing the average emission power of the laser over the entire working period and meeting the requirements for eye protection.

[0005] In order to achieve a large emission power in a very short time (usually nanoseconds), the laser needs to obtain a large current rise rate, and the driving circuit used to drive the VCSEL laser becomes the bottleneck that limits the current rise rate of the laser.

[0006] Therefore, a new type of driving circuit system for VCSEL lasers is needed. Summary of the Invention

[0007] One advantage of this application is that it provides a driving circuit system for a VCSEL cell, wherein the driving circuit system uses an energy storage inductor as an energy storage element and utilizes the principle that the current flowing through the energy storage inductor cannot change abruptly to construct the circuit system, so that the driving circuit system can drive the VCSEL cell to meet the preset requirements under the premise of using a low-voltage DC power supply as the power supply, and the voltage of the DC power supply is lower than the safe voltage value.

[0008] Another advantage of this application is that it provides a driving circuit system for VCSEL cells, wherein, since the driving circuit system uses a low-voltage DC power supply as the power supply, the circuit design adapted to the power supply in the driving circuit system is simplified.

[0009] Another advantage of this invention is that it provides a driving circuit system for a VCSEL cell, wherein the peak operating current of the VCSEL cell can be determined by adjusting the on-time of the field-effect transistor. That is, the driving circuit system has superior adjustability.

[0010] To achieve at least one of the above advantages or other advantages and objectives, according to one aspect of this application, a driving circuit system for a VCSEL cell is provided, comprising:

[0011] A charging circuit module, a driving circuit module, and a field-effect transistor electrically connected to the charging circuit module and the driving circuit module, wherein the driving circuit module is configured to provide operating current to the VCSEL unit;

[0012] The charging circuit module includes: a power supply unit and an energy storage inductor connected in series with the power supply unit, wherein the energy storage inductor is connected in series with the field-effect transistor;

[0013] The driving circuit module includes: a filter capacitor and a parasitic inductor connected in parallel with the filter capacitor, wherein the filter capacitor is connected in parallel with the field-effect transistor, and the parasitic inductor is connected in series with the energy storage inductor;

[0014] The field-effect transistor is configured to operate switchably between a cutoff position and a conduction position. When the field-effect transistor is in the conduction position, the power supply unit of the charging circuit module charges the energy storage inductor. When the field-effect transistor is in the cutoff position, the charged energy storage inductor provides current to the filter capacitor and the parasitic inductor, respectively. The reverse electromotive force of the energy storage inductor increases the voltage acting on the VCSEL unit, so that the operating current flowing through the VCSEL unit reaches a predetermined value within a predetermined rise time.

[0015] In the driving circuit system for VCSEL cells according to this application, the voltage value of the power supply unit is less than or equal to 24V.

[0016] In the driving circuit system for VCSEL cells according to this application, the voltage value of the power supply unit is 1V to 3V.

[0017] In the driving circuit system for VCSEL cells according to this application, the inductance of the energy storage inductor is from 5nH to 20nH.

[0018] In the driving circuit system for VCSEL cells according to this application, the energy storage inductor is formed by printed circuit technology.

[0019] In the driving circuit system for a VCSEL cell according to this application, the peak value of the operating current of the VCSEL cell can be controlled by the time the field-effect transistor is in the on position.

[0020] In the driving circuit system for VCSEL cells according to this application, the predetermined rise time is less than or equal to 2ns.

[0021] In the driving circuit system for VCSEL cells according to this application, the driving circuit module further includes a parasitic capacitance between the drain and source of the field-effect transistor connected in parallel with the filter capacitor.

[0022] In the driving circuit system for a VCSEL cell according to this application, the driving circuit module further includes a damping resistor configured to be connected in series with the VCSEL cell, wherein when the field-effect transistor is in the off position and the operating current flowing through the VCSEL cell approaches 0, the parasitic capacitance of the VCSEL cell, the filter capacitor, the parasitic inductance, and the damping resistor form an LCR series resonant circuit.

[0023] In the driving circuit system for VCSEL cells according to this application, the parasitic inductance is formed by the package of the VCSEL cell and the traces of the printed circuit board.

[0024] The further objects and advantages of the invention will become fully apparent from the following description and accompanying drawings.

[0025] These and other objects, features and advantages of the present invention will be fully realized through the following detailed description, drawings and claims. Attached Figure Description

[0026] Figure 1 The figure shows a block diagram of a driving circuit system for a VCSEL cell according to an embodiment of the present application.

[0027] Figure 2 The figure shows a schematic diagram of a driving circuit system for a VCSEL cell according to an embodiment of this application.

[0028] Figure 3 The figure shows a waveform diagram of the current flowing through the field-effect transistor and the current flowing through the VCSEL cell in a driving circuit system for a VCSEL cell according to an embodiment of the present application.

[0029] Figure 4 The figure shows a schematic diagram of the current change curve flowing through the VCSEL unit when the energy storage inductor discharges.

[0030] Figure 5 The diagram illustrates a schematic of an existing capacitor-storage type VCSEL drive circuit.

[0031] Figure 6 The diagram illustrates another existing capacitor-based VCSEL drive circuit. Detailed Implementation

[0032] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0033] Application Overview

[0034] As mentioned above, for lidar, the emission power of the laser determines the ranging range, while eye protection requirements limit the power of the lidar. To resolve this contradiction, it is necessary to have a large emission power of the laser within an extremely short pulse time, and at the same time, reduce the duty cycle of the pulse time, thereby reducing the average emission power of the laser throughout the entire working period and meeting the requirements for eye protection.

[0035] In order to achieve a large emission power in a very short time (usually nanoseconds), the laser needs to obtain a large current rise rate, and the driving circuit used to drive the VCSEL laser becomes the bottleneck that limits the current rise rate of the laser.

[0036] In other words, while improving the ranging accuracy of lidar, it is also necessary to meet the requirements of human eye protection. Achieving a high luminous power from a VCSEL laser in a very short time presents a challenge to the design of the drive circuit.

[0037] The existing driving circuits for VCSELs are capacitor-based VCSEL driving circuits. Figure 5 The diagram illustrates a schematic of a conventional capacitor-storage type VCSEL drive circuit. In such... Figure 5 In the driving circuit shown, V a1 and V a2 Indicator power supply, D a Indicates VCSEL, L a Indication of parasitic inductance, M a Indicator semiconductor power transistor, C a Indicator capacitor, R a Indicator resistor. When the semiconductor drive transistor M... a When in the off state, the current released by the power source flows through resistor R. a The following is capacitor C. a Charging. When the semiconductor driver transistor M... a When in the on state, capacitor C a To provide charge for driving the VCSEL laser. Resistor R a Limit the voltage across capacitor Ca to prevent excessive current from flowing through the VCSEL and damaging it if the VCSEL is turned on for an extended period.

[0038] Figure 6 The diagram illustrates another existing capacitor-based VCSEL drive circuit. (In...) Figure 6 In the driving circuit shown, V b1 and V b2 Indicator power supply, D b Indicates VCSEL, L b Indication of parasitic inductance, M b Indicator semiconductor power transistor, C b Indicator capacitor, R b A resistor is shown. In this drive circuit, the resistor R... b Used to limit the peak current that allows the VCSEL cell to conduct, and resistor R b In the semiconductor power transistor M b From being turned on to being turned off, it suppresses unnecessary resonance caused by parasitic capacitance and parasitic inductance.

[0039] Since the parasitic inductance introduced by the VCSEL cell package and PCB traces cannot be reduced indefinitely (that is, there is a lower limit to the parasitic inductance in the actual driving circuit), when the rise time of the VCSEL cell's operating current (here, rise time represents the time it takes for the operating current to jump from 0 to its peak value) is required to be on the order of nanoseconds, the influence of the parasitic inductance caused by the driving circuit itself can no longer be ignored.

[0040] In such Figure 5 and Figure 6In the illustrated capacitor-based VCSEL driver circuit, the current flowing through the VCSEL cell is equal to the current flowing through the parasitic inductance. According to Ohm's law for inductance:

[0041]

[0042] The current flowing through an inductor can be expressed as:

[0043]

[0044] It is evident that the current flowing through the inductor is the integral of the voltage across the inductor with respect to time. To make the current rise faster, i.e., to accelerate the rise time, the voltage across the inductor needs to be increased. This can be achieved by increasing the DC power supply voltage V. a1 and V a2 (V b1 and V b2 The voltage of ) can indirectly increase the parasitic inductance L a (L b The voltage across the two ends increases the rising edge of the current.

[0045] However, methods to increase the voltage of a DC power supply to achieve a faster rise time present some technical challenges in practical applications. Typically, this is achieved by using a DC-DC converter to increase the DC power supply voltage. Higher voltages pose challenges to the design of these DC-DC converters. Using a boost DC-DC converter as the power supply module can convert low voltage to high voltage, but this increases circuit complexity and consequently raises the weight, size, and cost of the drive circuitry.

[0046] Furthermore, while increasing the voltage of the DC power supply, the higher DC voltage often exceeds the specified safe voltage for the human body (the industry standard for safe voltage is no higher than 36V, and the safe voltage for continuous contact is 24V), posing a potential safety hazard. In other words, the technical solution of increasing the rise time by increasing the supply voltage has an upper limit. Once the safe voltage is exceeded, even if the rise time meets the preset requirements, it will be difficult to apply in some industries.

[0047] To address the aforementioned technical problems, the inventors of this application devise a circuit system that uses an energy storage inductor as an energy storage element and utilizes the principle that the current flowing through the energy storage inductor cannot change abruptly. This enables the driving circuit system to drive the VCSEL unit to meet preset requirements while using a low-voltage DC power supply as the power source.

[0048] Based on this, this application proposes a driving circuit system for a VCSEL cell, comprising: a charging circuit module, a driving circuit module, and a field-effect transistor electrically connected to the charging circuit module and the driving circuit module, wherein the driving circuit module is configured to provide operating current to the VCSEL cell; the charging circuit module includes: a power supply unit and an energy storage inductor connected in series with the power supply unit, wherein the energy storage inductor is connected in series with the field-effect transistor; the driving circuit module includes: a filter capacitor and a parasitic inductor connected in parallel with the filter capacitor, wherein the filter capacitor is connected in parallel with the field-effect transistor. The parasitic inductance is connected in parallel with the energy storage inductance in series; wherein the field-effect transistor is configured to operate switchably between a cutoff position and a conduction position; wherein when the field-effect transistor is in the conduction position, the power supply unit of the charging circuit module charges the energy storage inductance; wherein when the field-effect transistor is in the cutoff position, the charged energy storage inductance provides current to the filter capacitor and the parasitic inductance respectively, and the back electromotive force of the energy storage inductance increases the voltage acting on the VCSEL unit so that the operating current flowing through the VCSEL unit reaches a predetermined value with a predetermined rise time.

[0049] Hereinafter, exemplary embodiments according to this application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments of this application. It should be understood that this application is not limited to the exemplary embodiments described herein.

[0050] Exemplary driving circuit system

[0051] Reference manual attached Figure 1 To be continued Figure 3 A driving circuit system 300 for a VCSEL cell according to an embodiment of this application is described, wherein the driving circuit system 300 drives the VCSEL cell. In this application, the VCSEL cell may represent a single VCSEL laser or a VCSEL array formed by multiple VCSEL lasers, and is not limited thereto.

[0052] like Figure 1 As shown in the embodiment of this application, the driving circuit system 300 includes a charging circuit module 10, a driving circuit module 20, and a field-effect transistor 30 electrically connected to the charging circuit module 10 and the driving circuit module 20. The field-effect transistor 30 serves as a switching device to switch the driving circuit system 300 between a charging single-channel module in a working state and a driving circuit module in a working state. The driving circuit module 20 is used to provide operating current to the VCSEL unit.

[0053] Specifically, such as Figure 2 As shown, the charging circuit module includes: a power supply unit (e.g., such as...) Figure 2 (as shown in V1 and V2) and the energy storage inductor connected in series with the power supply unit (e.g., as shown in V1 and V2) Figure 2 As shown in L1), wherein the energy storage inductor and the field-effect transistor (e.g., as shown in L1) Figure 2 The M1 shown is connected in series. The drive circuit module includes: a filter capacitor (e.g., such as...) Figure 2 The C1 shown is shown in the figure, and the parasitic inductance connected in parallel with the filter capacitor (e.g., as shown in the figure). Figure 2 As shown in the diagram (L2), the filter capacitor is connected in parallel with the field-effect transistor, and the parasitic inductance is connected in series with the energy storage inductance. The driving circuit module is used to drive the VCSEL unit (e.g., as shown in the diagram). Figure 2 As shown in the figure (D), the VCSEL unit is connected in series with the parasitic inductor.

[0054] It is worth mentioning that, in such Figure 2 In the illustrated drive circuit system, L2 only indicates the parasitic inductance formed by the package of the VCSEL unit and the traces on the printed circuit board, and does not represent an inductor element connected to the drive circuit system.

[0055] During operation, the field-effect transistor (FET) is configured to switch between a cutoff position and a conduction position. When the FET is in the conduction position, the power supply unit of the charging circuit module charges the energy storage inductor. When the FET is in the cutoff position, the charged energy storage inductor provides current to the filter capacitor and the parasitic inductor, respectively. The back electromotive force of the energy storage inductor increases the voltage acting on the VCSEL cell, causing the operating current flowing through the VCSEL cell to reach a predetermined value within a predetermined rise time. The charged filter capacitor can be used to limit the voltage between the drain and source of the FET, preventing the FET from being damaged.

[0056] More specifically, when the field-effect transistor is in the ON position, the filter capacitor, the parasitic inductor, and the VCSEL unit are short-circuited, and the power supply unit of the charging circuit module charges the energy storage inductor. Ignoring the on-resistance of the field-effect transistor, the current flowing through the energy storage inductor can be expressed as:

[0057]

[0058] The energy stored in the energy storage inductor can be expressed as:

[0059]

[0060] As can be seen from the formula, the energy stored in the energy storage inductor is related to the inductance of the energy storage inductor and the magnitude of the charging current. Furthermore, the magnitude of the charging current flowing through the energy storage inductor is related to the voltage value of the power supply unit, the charging time, and the inductance of the energy storage inductor. More specifically, in the technical solution of this application, the peak value of the charging current can be controlled by the time the field-effect transistor is in the on position; that is, the peak value of the charging current can be controlled by the charging time. In other words, when the charging time of the energy storage inductor reaches a preset time, the current flowing through the energy storage inductor reaches its peak value.

[0061] Figure 3 This illustrates the waveform of the current flowing through the field-effect transistor when the power supply unit charges the energy storage inductor. For example... Figure 3 As shown, when the inductance of the energy storage inductor is 10nH and the peak current during charging is 10A, the conduction time of the field-effect transistor is 100ns.

[0062] When the field-effect transistor is in the off position, the driving circuit module discharges the VCSEL cell. Specifically, in the initial stage of the discharge of the energy storage inductor, due to the principle that the current flowing through the energy storage inductor cannot change abruptly, the inductor current flowing out of the energy storage inductor will not change abruptly. Furthermore, due to the presence of the parasitic inductance, it will suppress the current generated by the energy storage inductor from flowing directly to the VCSEL cell. Therefore, in the initial stage of discharge, most of the current flows through the filter capacitor, causing the voltage across the VCSEL cell to rise sharply. This accelerates the rise time of the operating current flowing through the VCSEL cell, that is, it increases the rise time of the VCSEL cell.

[0063] In other words, in this embodiment, the driving circuit system utilizes the principle that the current flowing through the energy storage inductor cannot change abruptly to construct the circuit, so that the operating current flowing through the VCSEL unit can reach a predetermined value with a predetermined rise time. Here, the predetermined value represents the required operating current value of the VCSEL unit. Quantitatively, in this embodiment, the predetermined rise time is less than or equal to 2ns.

[0064] Figure 4The diagram illustrates the current flow curve through the VCSEL unit when the energy storage inductor discharges. Specifically, since the current flowing through the energy storage inductor cannot change abruptly, when the field-effect transistor is turned off, the current flowing through the energy storage inductor must have a low-impedance path to release the current, causing the voltage across the filter capacitor to rise rapidly. Furthermore, this causes a momentary high voltage to be obtained across the circuit formed by the VCSEL unit and the parasitic inductor connected in series, ultimately resulting in a sharp increase in the current flowing through the VCSEL unit within a very short time. Figure 4 As shown.

[0065] As mentioned above, the inductor current provided by the energy storage inductor is related to the voltage value of the power supply unit, the charging time, and the inductance of the energy storage inductor. Specifically, according to the formula, it is directly proportional to the voltage value of the power supply unit and the charging time, and inversely proportional to the inductance of the energy storage inductor. Therefore, in this embodiment, the rise time of the VCSEL unit can be adjusted by adjusting the voltage value of the power supply unit, the charging time, and the inductance of the energy storage inductor.

[0066] Furthermore, if the inductance of the energy storage inductor can be reduced, the voltage of the power supply unit can be effectively reduced while achieving the same rise time. In this embodiment, the inductance of the energy storage inductor is 5nH to 20nH. Under this condition, the voltage of the power supply unit can be lower than the safe voltage, i.e., less than 24V. In particular, in the technical solution of this application, the voltage of the power supply unit can be set between 1V and 3V. Specifically, when the voltage of the power supply unit is between 1V and 3V, the design difficulty of the power supply unit can be reduced, thereby reducing costs.

[0067] It is worth noting that such a small inductance value makes the energy storage inductor difficult to manufacture precisely. In the embodiments of this application, the energy storage inductor is formed using a printed circuit board process, that is, the energy storage inductor is pre-installed on the PCB board during the circuit design stage. Specifically, the inductance value of the energy storage inductor can be controlled by controlling the length and shape of the traces on the printed circuit board, which not only simplifies the inductor design but also saves costs.

[0068] It is also worth mentioning that, in other examples of this application, the voltage value of the power supply unit and the inductance of the energy storage inductor can be adjusted according to the actual application, and this is not limited to this application.

[0069] It is worth noting that during the discharge process of the energy storage inductor, although the voltage of the field-effect transistor may exceed 100V (i.e., the voltage of the filter capacitor), and even approach 200V, the duration of such high voltage is extremely short, and its effect is far less than that corresponding to the electrostatic discharge model of the human body. It is also worth noting that the driving circuit module further includes the parasitic capacitance between the drain and source of the field-effect transistor connected in parallel with the filter capacitor.

[0070] Furthermore, in this embodiment, the driving circuit module further includes a damping resistor configured to be connected in series with the VCSEL unit (e.g., as shown in the image). Figure 2 (as shown in R1). The inventors of this application have discovered that when the field-effect transistor is in the off position and the operating current flowing through the VCSEL cell approaches 0 from its maximum value, the parasitic capacitance of the VCSEL cell, the filter capacitor, the parasitic inductance, and the damping resistor form an LCR series resonant circuit. The damping resistor is used to adjust the resonance of the LCR loop so that the LCR series resonant circuit does not have excessively long residual oscillation.

[0071] In summary, the driving circuit system for VCSEL cells based on the embodiments of this application is explained. The driving circuit system uses an energy storage inductor as an energy storage element and utilizes the principle that the current flowing through the energy storage inductor cannot change abruptly to construct the circuit system. This enables the driving circuit system to drive the VCSEL cell to meet the preset requirements in the presence of a low-voltage DC power supply, where the voltage of the DC power supply is lower than the safe voltage value.

[0072] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are merely examples and do not limit the present invention. The objectives of the present invention have been fully and effectively achieved. The functions and structural principles of the present invention have been shown and explained in the embodiments, and any modifications or variations of the embodiments of the present invention may be made without departing from the stated principles.

Claims

1. A driving circuit system for a VCSEL cell, for driving the VCSEL cell, characterized in that, include: A charging circuit module, a driving circuit module, and a field-effect transistor electrically connected to the charging circuit module and the driving circuit module, wherein the driving circuit module is configured to provide operating current to the VCSEL unit; The charging circuit module includes: a power supply unit and an energy storage inductor connected in series with the power supply unit, wherein the energy storage inductor is connected in series with the field-effect transistor; The driving circuit module includes: a filter capacitor, wherein the filter capacitor is connected in parallel with the field-effect transistor; the filter capacitor is connected in parallel with the VCSEL unit and the parasitic inductance formed by the VCSEL unit; the parasitic inductance is connected in series with the energy storage inductor; and the parasitic inductance is connected in series with the VCSEL unit. The field-effect transistor (FET) is configured to operate switchably between a cutoff position and a conduction position. When the FET is in the conduction position, the power supply unit of the charging circuit module charges the energy storage inductor. When the FET is in the cutoff position, the charged energy storage inductor discharges, providing current to the filter capacitor and the parasitic inductor. In the initial stage of the energy storage inductor's discharge, the parasitic inductor suppresses the current generated by the energy storage inductor from flowing directly to the VCSEL unit, causing most of the current generated by the energy storage inductor to flow through the filter capacitor. This causes the voltage across the VCSEL unit connected in parallel with the filter capacitor to rise sharply, increasing the back electromotive force of the energy storage inductor and thus increasing the voltage acting on the VCSEL unit. Consequently, the operating current flowing through the VCSEL unit reaches a predetermined value within a predetermined rise time; the predetermined rise time is less than or equal to 2 ns. The filter capacitor is connected between the source and drain of the field-effect transistor. The driving circuit module further includes a damping resistor configured to be connected in series with the VCSEL cell, wherein when the field-effect transistor is in the off position and the operating current flowing through the VCSEL cell approaches 0, the parasitic capacitance of the VCSEL cell, the filter capacitor, the parasitic inductance, and the damping resistor form an LCR.

2. The driving circuit system for a VCSEL unit according to claim 1, wherein, The voltage of the power supply unit is less than or equal to 24V.

3. The driving circuit system for a VCSEL unit according to claim 2, wherein, The voltage of the power supply unit is 1V to 3V.

4. The driving circuit system for a VCSEL unit according to claim 3, wherein, The inductance of the energy storage inductor is from 5nH to 20nH.

5. The driving circuit system for a VCSEL unit according to claim 4, wherein, The energy storage inductor is formed using a printed circuit process.

6. The driving circuit system for a VCSEL unit according to claim 1, wherein, The peak operating current of the VCSEL cell can be controlled by the timing of the field-effect transistor being in the on position.

7. The driving circuit system for a VCSEL cell according to claim 1, wherein, The driving circuit module further includes a parasitic capacitance between the drain and source of the field-effect transistor connected in parallel with the filter capacitor.

8. The driving circuit system for a VCSEL unit according to claim 1, wherein, The parasitic inductance is formed by the packaging of the VCSEL cell and the traces on the printed circuit board.

Images